Method and device for adjusting the braking and/or drive effects on wheel of motor vehicles

ABSTRACT

The present invention relates to a method and a device for adjusting the braking effect and/or driving effect at the wheels of a motor vehicle. For this purpose, a tire tolerance adjustment has at least two different operating modes. It is determined whether a mounted spare wheel or temporary spare wheel is present. One of the operating modes is selected as a function of the determined existence of a spare wheel.

BACKGROUND INFORMATION

[0001] The present invention relates to a method and a device having the features according to the definitions of the species in the independent claims.

[0002] A plurality of systems for anti-lock braking control, for traction control, and/or for vehicle stability in motor vehicles are known from the related art. These systems generally start from at least the wheel rotational speeds or the wheel speeds of the vehicle wheels. However, before the wheel speeds are used for regulation, they are generally corrected by a so-called tire tolerance adjustment. Such a regulating system for a motor vehicle is described in DE 42 30 295 A1, for example, in which errors in the wheel speeds created by tolerances between the tires are equalized. Such tolerances are due to different wheel diameters, for example. For example, a low-pass filtering in conjunction with a tire tolerance adjustment is described in DE 42 30 295 A1.

[0003] Furthermore, a slip regulation system is known, for example, from EP 0 510 466 A1, where the wheel rotational speeds are used for slip formation. To equalize the tire tolerances, the wheel speeds are corrected. When determining the appropriate correction factors, possibly existing cornering of the vehicle must be taken into consideration.

[0004] The variations for adjusting tire tolerances known from the related art generally require relatively long time intervals. If the braking regulation and/or driving regulation is acted upon shortly after the vehicle is started, a slow tire tolerance adjustment can potentially result in unfavorable conditions.

[0005] If there is tire damage on a motor vehicle, often only a temporary spare wheel or spare wheel is provided. In contrast to standard wheels, this temporary spare wheel or spare wheel has a significantly smaller diameter which is to be taken into consideration by a tire tolerance adjustment. A detection of such temporary spare wheels or spare wheels is known from EP 0 449 845 B1, for example.

SUMMARY OF THE INVENTION

[0006] As mentioned, the present invention relates to a method and a device for adjusting the braking effect and/or driving effect at the wheels of a motor vehicle. Assigned to the wheels are sensors that emit speed signals representing the rotary motions of the wheels. These speed signals are corrected via a correction, i.e., the tire tolerance adjustment. The braking and/or driving effect is/are adjusted at least as a function of corrected sensor speed signals.

[0007] The essence of the present invention is that the correction, i.e., the tire tolerance adjustment, has at least two different modes of operation. Furthermore, it is determined whether a mounted spare wheel or temporary spare wheel having a smaller diameter than the remaining wheels is present. One of the operating modes is then selected in accordance with the present invention, as a function of the determined existence of a spare wheel.

[0008] According to the present invention, a selection module is connected in series with and upstream from the actual tire tolerance adjustment, the selection module selecting a specific operating mode in response to a temporary spare wheel being present. This certain operating mode of the tire tolerance adjustment advantageously enables a particularly quick tire tolerance adjustment. The actual, slow tire tolerance adjustment, which is, however, generally more precise, follows the first, quick tire tolerance adjustment. As a result of this adjustment algorithm, the rotational speed of a temporary spare wheel or spare wheel is very quickly adjusted to the other wheel speeds. As a result of the present invention, the temporary spare wheel adjustment is carried out in such a manner that the complete functionality of an anti-lock control system, traction control system, and/or vehicle stability system or of an electronic braking force distribution system is already present when braking for the first time. Thus, no additional measures are necessary.

[0009] In an advantageous embodiment of the present invention, it is provided that the correction, i.e., the tire tolerance adjustment, is carried out more quickly in a first operating mode having a smaller filtering time constant than in a second operating mode having a larger filtering time constant.

[0010] A further embodiment of the present invention start from the assumption that the standard, slow tire tolerance adjustment is carried out as a function of the output torque of the vehicle engine. This can be inferred, for example, from the document DE 42 30 295 A1 mentioned at the outset. Thus, for the standard, i.e., slow, tire tolerance adjustment, a certain condition must be given for the engine torque in order for the tire tolerance adjustment to be carried out. For example, the drive torque or the drag torque acting on the wheels must be sufficiently low. However, this condition slows the tire tolerance adjustment in cases in which the engine torque does not satisfy this condition. According to this embodiment of the present invention, it is provided that the correction is carried out in a first, quick operation mode of the tire tolerance adjustment, independently of the engine torque.

[0011] It is further known to attach the tire tolerance adjustment to the condition that no cornering exists. In an additional embodiment of the present invention, it is provided that it be determined whether the vehicle is traveling on a curve. The essence of this embodiment is that the tire tolerance adjustment is performed in the first, quick operating mode, independently of determined cornering.

[0012] In a further embodiment of the present invention, it is provided that, in the first, quick operating mode, the tire tolerance adjustment is performed at lower forward speeds of the vehicle than in a second, slower operating mode.

[0013] However, the determination of whether there is a mounted temporary spare wheel or spare wheel is advantageously only begun when a predefinable speed threshold value for the vehicle's forward speed is exceeded.

[0014] In a further advantageous embodiment of the present invention, it is provided that the determination of whether there is a mounted temporary spare wheel or spare wheel occurs in such a manner that

[0015] the wheel having the highest rotational speed is determined from the speed signals;

[0016] a check is performed to determine whether the rotational speed of the wheel having the highest rotational speed deviates in a predefinable manner from the rotational speed having the speed of at least one other wheel, in particular of the wheel mounted on the same vehicle axle;

[0017] it is determined from the differences of the rotational speeds of the wheels on the axle on which the wheel having the highest rotational speed is not mounted whether cornering exists; and

[0018] the wheel having the highest rotational speed is determined as the temporary spare wheel or spare wheel provided that the rotational speed of this wheel deviates in a predefinable manner and especially for a predefinable period of time from the rotational speed of at least one other wheel, and there is no cornering.

[0019] In a further embodiment of the present invention, it is provided that the mode selected when a temporary spare wheel or spare wheel is present is terminated as a function of the result of a comparison of the corrected output signal of the temporary spare wheel or the spare wheel to an output signal of at least one sensor at another wheel. This is because the quick and tolerant tire tolerance adjustment is only intended to enable a first, quick adaptation of the temporary spare wheel to the reference wheel. The standard tire tolerance adjustment including its release conditions is to subsequently apply again. The quick and tolerant tire tolerance adjustment is, therefore, ended when the rotational speed of the temporary spare wheel or spare wheel deviates less than 1.5%, for example, from the other wheel rotational speeds.

[0020] Additional advantageous embodiments are given in the dependent claims.

BRIEF DESCRIPTION OF THE DRAWING

[0021]FIG. 1 shows an overview of a block diagram of the present invention. FIG. 2 shows the basic sequence of the adjustment of the braking effect and/or driving effect at the wheels, while FIG. 3 shows the detailed sequence of a specific embodiment of the present invention.

EXEMPLARY EMBODIMENT

[0022] Embodiments of the present invention are described below in light of the exemplary embodiments.

[0023]FIG. 1 shows a schematic view of a vehicle having vehicle wheels 101 ij. In the following, the index i designates the association of the corresponding quantity with the rear (i=h) or the front (i=v) vehicle axle. The index j indicates the association of the corresponding quantity with the right (j=r) or the left (j=l) side of the vehicle. Speed sensors 105 ij and wheel brake units 106 ij are mounted on vehicle wheels 101 ij. Wheel speed sensors 105 ij send their output signals Nij to control unit 104. In control unit 104, drive signals Bij for wheel brake units 106 ij are formed at least as a function of wheel speed values Nij. This occurs in a generally known manner, for example, by forming slip values for individual vehicle wheels 101 ij from wheel speeds Nij, the braking effect and/or the driving effect at the individual vehicle wheels being subsequently adjusted via signals Bij and/or A in such a manner that a specific brake slip or drive slip is not exceeded.

[0024] In addition, the vehicle's drive train is sketched in FIG. 1. In this context, reference numeral 103 designates the vehicle engine whose output power or output torque or output rotational speed can be controlled or regulated via control unit 104, using drive signal A. The output torque of engine 103, which, in engine management, generally exists as torque signal Mmot, is directed to control unit 104.

[0025] Vehicle engine 103 is connected to transmission 105 via clutch 108. Transmission 105 is then connected via differential 102 to the drive gears on the back axle. The output rotational speed of the transmission is determined via speed sensor 107. Corrected by the transmission ratio of differential 102 and/or by the wheel diameter at the driving wheels, the output rotational speed of the transmission is a measure of forward speed V of the vehicle.

[0026] The adjustment of the braking and/or driving effect at vehicle wheels 101 ij via control unit 104 is shown schematically in FIG. 2. After initial step 201, wheel speed signals Nij and additional signals are detected in following step 202. In step 203, the drive signals for wheel brakes 106 ij (drive signal Bij) and drive signal A for vehicle engine 103 are formed at least as a function of detected wheel speed signals Nij. This is indicated in step 203 by functional dependence F and G. After final step 204, the sequence shown in FIG. 2 is restarted. The formation of drive signals Bij and A is described frequently in the related art and will not be explained in greater detail here.

[0027]FIG. 3 shows a detailed sequence of an exemplary embodiment according to the present invention.

[0028] After start step 301, counter value T is first set to zero in step 302. In step 303, wheel speeds Nij or the vehicle's forward speed is/are determined.

[0029] In query 304, forward speed V of the vehicle is compared to a threshold value SW1. If forward speed V of the vehicle does not exceed threshold value SW1, the following conditions for quick tire tolerance adjustment 309 are not checked. In this case, standard tire tolerance adjustment 310 including its special acceptance conditions (e.g. conditions for the engine torque, cornering, etc.) is carried out.

[0030] However, if forward speed V of the vehicle does exceed threshold value SW1, the vehicle is traveling at a sufficiently high vehicle speed, whereupon the fastest rotating wheel is determined in step 305. This wheel exhibits non-corrected wheel speed Nfast. Furthermore, non-corrected wheel speed Nref of the other wheel of the same axle (reference wheel) is loaded into a temporary register for further processing.

[0031] In addition, a tolerance band Tb is formed in step 305. Predefinable threshold values SWu and SWo are provided for this purpose. Using wheel speed Nref of the reference wheel, tolerance band Tb is calculated in correspondence with the possibly mounted temporary spare wheels. For this purpose, a lower value SWu as well as an upper value SWo are added to wheel speed Nref of the reference wheel. In this manner, one obtains tolerance band Tb:

Tb=[(Nref+SWu);(Nref+SWo)]

[0032] Step 306 determines whether speed Nfast of the fastest wheel is within tolerance band Tb. If this is not the case, the fastest wheel is obviously not a temporary spare tire or spare tire. Standard tire tolerance adjustment 310 is then performed.

[0033] However, if step 306 determines that rotational speed Nfast is within the tolerance band, this wheel is a temporary spare wheel or a spare wheel. Subsequent step 307 then determines whether the vehicle is cornering at the moment. Cornering is checked for in light of the following condition.

[0034] The difference in the wheel speeds of the axle on which the supposed temporary spare wheel (fastest wheel) is not located must be less than or equal to a certain threshold value. If this is the case, it can be assumed that the vehicle is traveling on a curve having a larger radius of curve or is traveling straight. In this case, step 308 is the next step. However, if the vehicle is traveling on a curve having a small radius of curve, standard tire tolerance adjustment 310 including its special acceptance conditions is performed. If it is determined, for example, that the temporary spare wheel (fastest wheel) is located on the front axle, the amount of the rotational speed difference ΔN=|(Nhr−Nhl)| of the back wheels is compared to a relatively small threshold value SW3, which can, for example, be selected as a function of the vehicle's forward speed, in order to detect curves. If rotational speed difference ΔN is less than threshold value SW3, there is essentially no cornering. If rotational speed difference ΔN exceeds threshold value SW3, there is cornering.

[0035] To detect curves in step 307, a steering angle signal, a transverse acceleration signal, and/or a yaw angle signal can be used, provided that the appropriate sensors are present in or on the vehicle.

[0036] Query 308 determines whether counter value T exceeds a corresponding, predefinable threshold value SW2. If this is not the case, the counter value is increased by one counter value in step 311, and the already described sequence is restarted with step 303.

[0037] However, if step 308 determines that the counter value exceeds threshold value SW2, the conditions for quick tire tolerance adjustment 309 have been present for a sufficient length of time. In this case, quick tire tolerance adjustment 309 is performed.

[0038] The quick and tolerant tire tolerance adjustment 309 is only intended to enable a first, quick adaptation of the temporary spare wheel to the reference wheel. The standard tire tolerance adjustment including its release conditions is to subsequently apply again. This is achieved in that wheel speed Nfast of the temporary spare wheel is corrected to form corrected wheel speed Nfast,kor in step 313. In subsequent step 314, corrected value Nfast,kor is compared to rotational speed Nref of the reference wheel. As long as corrected value Nfast,kor is greater than reference rotational speed Nref, quick tire tolerance adjustment 309 is maintained. However, as soon as corrected value Nfast,kor exceeds rotational speed Nref of the reference rotational speed, the quick tire tolerance adjustment is terminated in final step 312. In step 314, the difference (Nfast,kor−Nref) can also be compared to a threshold value that is 1.5% of Nref, for example.

[0039] After the correction is terminated in operating mode RTA_(quick), this operating mode RTA_(quick) is blocked for at least a period of time. In particular, it can be provided that the blocking is maintained at least until the vehicle is started again. In this manner, a further, possibly incorrect, quick adjustment during the remaining drive is prevented. However, the blocking of this operating mode RTA_(quick) can be canceled or not induced when the existence of cornering is detected during operating mode RTA_(quick). In this case, mode RTA_(quick) continues to be allowed.

[0040] According to the present invention, a software module detects the typical speed difference of a temporary spare wheel or spare wheel with respect to other wheel rotational speeds. Certain conditions are then checked in accordance with the present invention:

[0041] The vehicle is traveling at a significantly high speed (query 303).

[0042] No additional wheel satisfies the temporary spare wheel or spare wheel condition.

[0043] A time criterion is satisfied (query 308).

[0044] If these conditions are satisfied, the subsequent tire tolerance adjustment module is modified, so that it is enabled as being tolerant and is quickly carried out until the temporary spare wheel is adjusted to a certain percentage. This occurs such that

[0045] the tire tolerance adjustment is begun upon initiating travel;

[0046] the tire tolerance adjustment is carried out independently of the engine torque;

[0047] the tire tolerance adjustment is carried out more quickly (smaller filtering time constant); and

[0048] the tire tolerance adjustment is carried out in a curve-tolerant manner, i.e., independently of whether cornering exists.

[0049] The quick and tolerant, tire tolerance adjustment is terminated when the rotational speed of the temporary spare wheel or spare wheel deviates less than 1.5%, for example, from the other wheel rotational speeds. By way of exception, the quick tire tolerance adjustment is repeated after cornering when this quick tire tolerance adjustment was performed before or during cornering.

[0050] As a result of the present invention, the temporary spare wheel adjustment is carried out in such a manner that the complete functionality of an anti-lock control system or of an electronic braking force distribution system is already present when braking for the first time. Thus, no additional measures are necessary.

[0051] In a further embodiment of the present invention, it is provided that a status signal is generated when a mounted temporary spare wheel or spare wheel is present. The functioning of other vehicle systems, such as systems for anti-lock brake control, for traction control, and/or for vehicle stability are modified as a function of this status signal.

[0052] In this context, it is particularly provided that the status signal is supplied via a data line, in particular via a bus system (CAN bus, Controller Area Network), to other vehicle systems for controlling and/or regulating vehicle functions. Thus, for example, provision can be made for the vehicle's forward speed to be limited when a temporary spare wheel or a spare wheel is detected.

[0053] Furthermore, the status signal can be used for triggering a display that can be observed by the driver. In the event that a temporary spare wheel or a spare wheel is present, this is displayed to the driver. As a result, the driver is continually reminded that a temporary spare wheel or a spare wheel is mounted.

[0054] Furthermore, monitoring means can be provided via which slip values of the wheels are measured and evaluated in such a manner that, given the existence of slip values of a certain, preselectable magnitude, predefinable measures are introduced. For example, in the case of such sustained slip monitoring, it can be provided that braking and/or driving systems are switched off when sufficiently high slip values have been present for a sufficient period of time. If these monitoring means evaluate the uncorrected wheel rotational speeds, the monitoring means are deactivated when a temporary spare wheel or a spare wheel is detected. 

What is claimed is:
 1. A method for adjusting the braking and/or driving effect at the wheels (101 ij) of a motor vehicle, having at least two wheels and having the sensors (105 ij), which are assigned to the wheels, and which generate speed signals (Nij) representing the rotary motions of the wheels, the speed signals (Nij) being corrected by a correction, and the braking and/or driving effect being adjusted at least as a function of the corrected output signals of the sensors, wherein the correction has at least two different operating modes (RTA_(normal), RTA_(quick)); and it is determined whether a mounted temporary spare wheel or spare wheel having a smaller radius than the remaining wheels is present; one of the modes (RTA_(normal), RTA_(quick)) is selected as a function of the ascertained presence of a temporary spare wheel or spare wheel.
 2. The method as recited in claim 1, wherein the correction is performed more quickly in a first operating mode (RTA_(quick)) having a smaller filtering time constant than in a second operating mode (RTA_(normal)) having a larger filtering time constant.
 3. The method as recited in claim 1, wherein the motor vehicle is driven by a vehicle engine (103), and the correction is performed in a second operating mode (RTA_(normal)), as a function of an engine quantity (Mmot) representing the output torque and/or the output power of the vehicle engine, and, in a first operating mode (RTA_(quick)), independently of the engine quantity.
 4. The method as recited in claim 1, wherein it is determined whether the vehicle is traveling on a curve, and the correction is performed in a second operating mode (RTA_(normal)), as a function of detected cornering, and, in a first operating mode (RTA_(quick)), independently of detected cornering.
 5. The method as recited in claim 1, wherein the forward speed (V) of the vehicle is determined, and the correction is performed in a first operating mode (RTA_(quick)), at a lower forward speed of the vehicle than in a second operating mode (RTA_(normal)).
 6. The method as recited in claim 1, wherein the vehicle's forward speed (V) is detected, and the determination of whether a mounted temporary spare wheel or spare wheel is present is begun in response to the exceeding of a predefinable speed threshold value (SW1).
 7. The method as recited in claim 1, wherein the determination of whether there is a mounted temporary spare wheel or spare wheel is made such that the wheel having the highest rotational speed is determined from the speed signals (Nij); a check is performed to determine whether the rotational speed (Nfast) of the wheel having the highest rotational speed deviates in a predefinable manner (Tb) from the rotational speed of at least one other wheel (Nref), in particular of the wheel mounted on the same vehicle axle; it is determined from the differences in the rotational speeds of the wheels on the axle on which the wheel having the highest rotational speed is not mounted whether cornering exists; and the wheel having the highest rotational speed is determined as the temporary spare wheel or spare wheel provided that the rotational speed (Nfast) of this wheel deviates in a predefinable manner and especially for a predefinable period of time (SW2) from the rotational speed (Nref) of at least one other wheel, and there is no cornering.
 8. The method as recited in claim 1, wherein the mode (RTA_(quick)), which is selected in response to the presence of a temporary spare wheel or spare wheel, is terminated as a function of a comparison of the corrected output signal of the temporary spare wheel or the spare wheel, to an output signal of at least one sensor at another wheel.
 9. The method as recited in claim 1, wherein, following termination of the correction in the operating mode (RTA_(quick)), which is selected when a mounted temporary spare wheel or spare wheel is present, this operating mode (RTA_(quick)) is blocked for at least a period of time, in particular, at least until the next time the vehicle is started.
 10. The method as recited in claim 9, wherein the blocking of this operating mode (RTA_(quick)) is canceled or not induced when it is determined during this operating mode (RTA_(quick)) that cornering exists.
 11. The method as recited in claim 1, wherein a status signal is generated when a mounted temporary spare wheel or spare wheel is present, and the functioning of other vehicle systems, such as systems for anti-lock brake control, for traction control, and/or for vehicle stability control are modified as a function of this status signal; provision being made in particular for the status signal to be supplied via a data line, in particular via a bus system, to other vehicle systems for controlling and/or regulating vehicle functions; and/or for the forward speed of the vehicle to be limited when a temporary spare wheel or a spare wheel is detected; and/or for the status signal to be used for triggering a display that can be observed by the driver, in the case of the presence of a temporary spare wheel or a spare wheel, this being indicated to the driver; and/or for monitoring means to be provided via which slip values of the wheels are measured and evaluated in such a manner that, given the existence of slip values of a specific, preselectable magnitude, predefinable measures are introduced, and the monitoring means are deactivated when the presence of a temporary spare wheel or of a spare wheel is detected.
 12. A device for adjusting the braking and/or driving effect at the wheels (101 ij) of a motor vehicle, having at least two wheels and having the sensors (105 ij), which are assigned to the wheels and which emit speed signals (Nij) representing the rotary motions of the wheels, the speed signals (Nij) being corrected by a correction, and the braking and/or driving effect being adjusted at least as a function of the corrected output signals of the sensors, wherein the correction has at least two different operating modes (RTA_(normal), RTA_(quick)); and it is determined whether a mounted temporary spare wheel or spare wheel having a smaller radius than the remaining wheels is present; one of the modes (RTA_(normal), RTA_(quick)) is selected as a function of the ascertained presence of a temporary spare wheel or spare wheel.
 13. The device as recited in claim 12, wherein the correction is performed more quickly in a first operating mode (RTA_(quick)) having a smaller filtering time constant than in a second operating mode (RTA_(normal)) having a larger filtering time constant; and/or the motor vehicle is driven by a vehicle engine (103), and the correction is performed in a second operating mode (RTA_(normal)) as a function of an engine quantity (Mmot) representing the output torque and/or the output power of the vehicle engine and, in a first operating mode (RTA_(quick)), independently of the engine quantity; and/or it is determined whether the vehicle is traveling on a curve, and the correction is performed in a second operating mode (RTA_(normal)), as a function of detected cornering and in a first operating mode (RTA_(quick)) independently of detected cornering; and/or the forward speed (V) of the vehicle is determined, and, in a first operating mode (RTA_(quick)), the correction is performed at a lower forward speed of the vehicle than in a second operating mode (RTA_(normal)); and/or the forward speed (V) of the vehicle is detected, and the determination of whether a mounted temporary spare wheel or spare wheel is present is begun in response to the exceeding of a predefinable speed threshold value (SW1).
 14. The device as recited in claim 12, wherein the determination of whether a mounted temporary spare wheel or spare wheel is present is made such that the wheel having the highest rotational speed is determined from the speed signals (Nij); a check is performed to determine whether the rotational speed (Nfast) of the wheel having the highest rotational speed deviates in a predefinable manner (Tb) from the rotational speed of at least one other wheel (Nref), in particular of the wheel mounted on the same vehicle axle; it is determined from the differences in the rotational speeds of the wheels on the axle on which the wheel having the highest rotational speed is not mounted whether cornering exists; and the wheel having the highest rotational speed is determined as the temporary spare wheel or spare wheel, provided that the rotational speed (Nfast) of this wheel deviates in a predefinable manner and especially for a predefinable period of time (SW2) from the rotational speed (Nref) of at least one other wheel, and there is no cornering.
 15. The device as recited in claim 13, wherein the mode (RTA_(quick)), which is selected in response to the presence of a temporary spare wheel or spare wheel, is terminated as a function of a comparison of the corrected output signal of the temporary spare wheel or the spare wheel to an output signal of at least one sensor at another wheel. 